Elevated temperature spectroscopic ellipsometry analysis of the dielectric function, exciton, band-to-band transition, and high-frequency dielectric constant properties for single-crystal ZnGa2O4

Matthew Hilfiker, Emma Williams, Ufuk Kilic, Yousra Traouli, Nate Koeppe, Jose Rivera, Assya Abakar, Megan Stokey, Rafał Korlacki, Zbigniew Galazka, Klaus Irmscher, Mathias Schubert

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Abstract

We report the elevated temperature (22 °C ≤ T ≤ 600 °C) dielectric function properties of melt grown single crystal ZnGa2O4 using a spectroscopic ellipsometry approach. A temperature dependent Cauchy dispersion analysis was applied across the transparent spectrum to determine the high-frequency index of refraction yielding a temperature dependent slope of 3.885(2) × 10-5 K-1. A model dielectric function critical point analysis was applied to examine the dielectric function and critical point transitions for each temperature. The lowest energy M0-type critical point associated with the direct bandgap transition in ZnGa2O4 is shown to red-shift linearly as the temperature is increased with a subsequent slope of-0.72(4) meV K-1. Furthermore, increasing the temperature results in a reduction of the excitonic amplitude and increase in the exciton broadening akin to exciton evaporation and lifetime shortening. This matches current theoretical understanding of excitonic behavior and critically provides justification for an anharmonic broadened Lorentz oscillator to be applied for model analysis of excitonic contributions.

Original languageEnglish (US)
Article number132105
JournalApplied Physics Letters
Volume120
Issue number13
DOIs
StatePublished - Mar 28 2022

ASJC Scopus subject areas

  • Physics and Astronomy (miscellaneous)

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